This invention relates to the system and methods for reducing torque for starting displacements of rotary or spherical hydraulic joints and making such displacements smooth. More particularly, this invention relates to a system and method for reducing torque for displacing anthropomorphically configured diving suits to decrease the effort to initiate motion, increase smoothness of motion, and delay the onset of diver fatigue.
Atmospheric Dive Suits (ADS) are one-man anthropromorphically configured submersibles designed for a diver at great water depths while the inside of the ADS remains at the surface pressure of one atmosphere. Rotary joints (spherical and/or cylindrical joints) are most likely to be used for arms and legs. Rotary joints produce arm and leg motions by having joints with surfaces that rotate relative to each other on a common surface. Typically, several rotary joints must be moved relative to each other to produce the desired arm or leg motion. Spherical joints have ball and socket like parts that rotate spherical surfaces spherically over a small arc. A chain of these joints allow arm and leg motion resembling surface locomotion of a human. To create arm or leg motion several might be actuated at once.
Rotary and spherical joints of an ADS both use hydraulic fluid in an oil cavity to provide separation and a bearing surface between the mechanical parts that are connected in limbs of the ADS. The hydraulic pressure in the oil cavity balances and resists the tendency of the water to crush the parts together. The hydraulic pressure is raised so that the surface area of the oil cavity between the mechanical components times the hydraulic pressure is equal to the displaced area of the mechanical components times the ambient pressure.
Rotary and spherical joints have another complicating requirement that makes them susceptible to startup friction, especially at depth. That is, the joints must be designed so that the size of the hydraulic cavity does not change with orientation. Otherwise, the exterior pressure would force the joint into a minimum volume configuration preventing motion.
Although an ADS removes the diver from the direct effect of water pressure, physical exertion to produce motion of the ADS can be tiring. The parasitic exertion is a result of friction from the seals and viscosity of the fluid. Consequently, less “exploratory” activity is likely due to the difficulty on making all joints move. The mass and the momentum of the ADS, and the water resistance required to move the limbs, combine to create inertia and drag resistive motion. A substantial startup-torque is needed to overcome these factors and makes operation physically exhausting. The problems associated with other rotary joints used in other specialized underwater applications, such as thrust vectoring nozzles for propulsors, or alignment joints for mating sections for manned transfer, also can have excessive resistance proportional to drag that must be overcome by increased force to begin their displacements.
Because of the large balancing forces involved to displace intricate joints in the ADS, the small deflections that occur with increasing depth tend to greatly increase the startup torque required to move the joints. This adversely affects a working diver, as each motion requires more effort. Divers tire faster, are limited in motion, and use up the life support faster. Replacing a diver at 2000 foot depths takes 35 minutes for the first diver to surface, a minimum of 30 minutes change-out (suit prep), and another 35 minutes for another diver to get back down, and this procedure wastes valuable time. With spherical joints, start up torque generally initiates start up motion one joint at a time, so that the start up friction load is only encountered as each joint starts to move. This problem is exacerbated for cylindrical type joints since several joints may need to be initiated simultaneously to make motion, making responsive motion even harder. At significant depths where small jobs needing precise motions are required, the excessive startup torque tends to produce erratic and unsmooth motions for both types of joints. Another limitation is that the inefficient work rates can reduce the life of the life support system. Also, unneeded work efforts can tax the ability of the carbon dioxide scrubbing system to remove the carbon dioxide from the suit adequately.
Thus, in accordance with this inventive concept, a need has been recognized in the state of the art for a system and method for reducing the torque needed to displacing limbs of an anthropomorphically configured diving suit to decrease the effort to initiate motion, increase smoothness of motion, delay the onset of diver fatigue, ensure smooth motion and reduce mechanically activated joints that can be large enough for a man to fit through.